<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button>点击</button>
    <script>
        var that;
        class Star {
            constructor(uname, age) {
                this.uname = uname;
                this.age = age;
                //this.sing();
                that = this;
                this.btn = document.querySelector('button');
                this.btn.onclick = this.sing;
            }
            sing() {
                console.log(this);
                console.log(that.uname);
            }
        }
        var ldh = new Star('ldh');
        // ldh.sing();
        console.log(that === ldh);
    </script>
</body>

</html>